CN1196123A - Multipath error reduction in spread spectrum receiver for ranging applications - Google Patents

Multipath error reduction in spread spectrum receiver for ranging applications Download PDF

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Publication number
CN1196123A
CN1196123A CN96196836A CN96196836A CN1196123A CN 1196123 A CN1196123 A CN 1196123A CN 96196836 A CN96196836 A CN 96196836A CN 96196836 A CN96196836 A CN 96196836A CN 1196123 A CN1196123 A CN 1196123A
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China
Prior art keywords
signal
prn
sign indicating
indicating number
mentioned
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CN96196836A
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Chinese (zh)
Inventor
马克·绍茨施基
维克多·威特塞尔
斯塔尼斯洛夫·斯拉诺维斯基
贾瓦德·阿施佳伊
里奥内尔·噶林
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MAGLAN Inc
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MAGLAN Inc
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Priority claimed from US08/512,822 external-priority patent/US5953367A/en
Application filed by MAGLAN Inc filed Critical MAGLAN Inc
Publication of CN1196123A publication Critical patent/CN1196123A/en
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S1/00—Beacons or beacon systems transmitting signals having a characteristic or characteristics capable of being detected by non-directional receivers and defining directions, positions, or position lines fixed relatively to the beacon transmitters; Receivers co-operating therewith
    • G01S1/02—Beacons or beacon systems transmitting signals having a characteristic or characteristics capable of being detected by non-directional receivers and defining directions, positions, or position lines fixed relatively to the beacon transmitters; Receivers co-operating therewith using radio waves
    • G01S1/04—Details
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/707—Spread spectrum techniques using direct sequence modulation
    • H04B1/7073—Synchronisation aspects
    • H04B1/7085—Synchronisation aspects using a code tracking loop, e.g. a delay-locked loop
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
    • G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
    • G01S19/13—Receivers
    • G01S19/22—Multipath-related issues
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
    • G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
    • G01S19/13—Receivers
    • G01S19/24—Acquisition or tracking or demodulation of signals transmitted by the system
    • G01S19/30—Acquisition or tracking or demodulation of signals transmitted by the system code related
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/707—Spread spectrum techniques using direct sequence modulation
    • H04B1/709—Correlator structure

Abstract

A receiver of a radio frequency signal having a pseudo-random noise (PRN) code, and techniques of processing such a signal that are especially adapted for ranging applications. A signal corresponding to the PRN code is locally generated and used for decoding the received signal in a manner to reduce ranging errors that can result when multipath (delayed) versions of the radio frequency signal are also present. A significant application of the receiver and signal processing techniques of the present invention is in a Global Positioning System (GPS), wherein a number of such signals from several satellites are simultaneously received and processed in order to obtain information of the position, movement, or the like, of the receiver. A delay locked loop (DLL) correlator, provided in each of the receiver's multiple processing channels, locks onto a line of sight signal from one of the satellites with the effect of any multipath signal(s) being significantly reduced.

Description

The reduction of the multipath error of the band spread receiver during range finding is used
The present invention relates to be used for the digital radio receiver of navigational system and other range finding application, wherein received signal adopts the sign indicating number of pseudo noise (PRN) class to encode.The present invention is specifically designed in the multipath fading serious environmental.
U.S. government has placed some satellites in orbit, is used as the part of GPS (GPS).A GPS receiver receives and comes from the signal of several these satellites, and can determine point-device parameter, for example orientation, speed and time etc.This technology has military and commercial purposes simultaneously.Main military use is to make receiver on aircraft or the steamer can determine the orientation and velocity of aircraft or steamer continuously.An example of commercial use comprises accurately the orientation of measuring and determining a point of fixity exactly, or the distance between two point of fixity.Another example is to be used for producing high-precision timing reference.
In order to realize this function, each satellite is constantly launched two L-band signal.Receiver detects these signals that comes from several different satellites simultaneously, and they are handled with information extraction from signal, so that calculate required parameter, and for example orientation, speed or time etc.U.S. government has adopted the standard of satellite transmits, so that make other people utilize these satellites by the receiver that foundation is used for specific purpose.The standard of relevant these satellite transmits has detailed elaboration in " interface control document " of RockWell international corporation, filename is " Navstar GPS Space Segment/Navigation User Interface (navigator's satellite GPS space segment/navigation user interface) ", date issued is on September 26th, 1984, is revised on Dec 19th, 1986.
Briefly, each satellite is typically expressed as 1540f at the carrier wave of 1575.42MHz 0, f wherein 0=1.023MHz, on send a L1 signal.The carrier frequency of second L2 signal being launched by each satellite is 1227.6MHz, or 1200f 0Each sort signal is being unique pseudo random signal FUNCTION MODULATION for this satellite by at least one in the satellite all.So just formed the spread-spectrum signal of opposing wireless frequency noise or artificial interference.The L-band signal that it also allows to come from a plurality of satellites is confirmed respectively in receiver and is separated.A this pseudo-random function is to L in satellite 1And L 2The precision encoding that carrier wave is modulated (" P-sign indicating number ").The clock frequency of P-sign indicating number is 10.23MHz, thereby makes L 1And L 2The bandwidth of signal is 20.46MHz.The length of this kind coding is 7 days; That is to say that the P-pattern restarted every 7 days.In addition, the L of each satellite 1Signal is by one second pseudo-random function or a unique accurate catch code (" C/A sign indicating number ") modulation; The clock frequency of C/A sign indicating number is 1.023MHz, and its pattern repeats once for every millisecond, promptly includes 1023 bits.And, L 1Carrier wave also is provided with the navigation data stream of 50 bits per seconds of some information such as satellite sign, state and modulates.
In receiver, in process, produced corresponding to the signal of known pseudo-random function to those satellite-signal demodulation, and with the phase alignment that is modulated to those signals on the satellite-signal.The phase place of the tracked carrier wave that comes from each satellite is to carry out relevant result by each satellite-signal with the local pseudo-random function that produces to record.The relative phase that comes from the carrier signal of some satellites is received the measurement parameter of machine as the final numerical value that is used for calculating required distance, speed, time etc.Because P-code encryption function (Y-sign indicating number) will be classified by U.S. government, so they can only use in military use, the commercial user of GPS must directly use C/A sign indicating number pseudo-random function.
Kremlin has been placed a global position system that similarly is called GLONASS in orbit; Relevant its more information of standard can find in RTCA reports " the GPS (Global Position System) GLONASS interface control document " of No.518-91/SC 159-317, by Glavkosmos Space Facilities engineering department, the GLONASS official of USSR (Union of Soviet Socialist Republics) is responsible for tissue, ratify.Although the present invention described herein is used for GPS System in USA, it also is applicable to and is designed to obtain the receiver of GLONASS signal or the radio system that any use PN (pseudo noise) sequence is found range.
One of the principal element of final accuracy that influences the measurement of resulting distance, speed etc. is the accuracy that signal phase is measured.If except direct line-of-sight propagation signal, also received a multipath fading signal, the precision of this phase measurement will change so.Such as, the phase place of C/A sign indicating number is determined that by a delay phase-locked loop (DLL) correlator wherein the phase place of the inner C/A PRN sign indicating number sequence that produces is adjusted, so that the error signal minimum in a control loop.DLL uses the leading-delay version of the inner sign indicating number that produces in a signal correction device, this correlator is the part of DLL.The time interval between the leading-delay version of a PRN code element of many this receivers uses.(one " code element " is this yard one+1 or time of being kept in-1 o'clock.) the work of DLL in this receiver will be subjected to the influence of any multipath signal that occurs, thereby produce tracking error.The condition of the phase locking of DLL is not only by in order to eliminate the control of the needed line-of-sight signal of phase measurement error, and is subjected to the influence of multipath signal.
Under the condition of out-phase, can make it to reduce by the delay interval that shortens between the leading delay correlator among the DLL by the error that multipath distortion produced.Although this technology is by reducing the loop gain of more weak multipath signal, what have reduced the influence of the multipath signal that is received, and the result of gained is still inaccurate.Postpone no matter what exists in the multipath signal, all can not fully eliminate tracking error by shortening the leading delay interval that postpones simply.
Therefore, main and a basic target of the present invention are further to reduce, even eliminate the phase measurement error that is produced in some cases when one or several multipath version of a PRN coded signal occurs.
It is that a DLL correlator by being provided is realized that this target of the present invention and other target are put it briefly, the PRN sign indicating number that this correlator produces this locality with from satellite or between the PRN sign indicating number of radio frequency, encoding that other source receives the loop gain that differs in most of scopes be zero; And meanwhile differ the loop gain that the district provides a limited size to being positioned near zero job that differs.Therefore, the effect of DLL is exactly to make the error signal of the received signal of a relative phase in narrow work phase window be kept to minimum, and not to be subjected to outside window loop gain be the influence of the multipath version of this signal in zero the zone.The present invention has represented a sign indicating number loop error, and this error is almost nil for multidiameter far away, has in fact eliminated the influence of multipath far away for the pseudo range measurement precision.This improvement is not that the performance with nearly multipath obtains as cost, although its performance classes is similar to the arrowband correlator in this case.
In a kind of form of the present invention, radiofrequency signal by allowing DLL catch as an arrowband correlator job, at this moment all has some gains at first in the whole scope that differs.When signal is when being hunted down on by the composite signal that DLL is locked onto line-of-sight signal and multipath signal, DLL provides loop gain with regard to only switching to a little central area, thereby identifies signal.
According to a concrete target of the present invention, this DLL response is provided by a plurality of leading-delay correlators with parallel connection of different leading-delay time delays that provided.Relevant result is by the arithmetic addition.The size of the working range of the center relative phase of loop response be by correlator selected specific leading-length of delay that postpones sets.Among the described hereinafter embodiment, used two correlators, the leading-delay that postpones of one of them correlator is 0.1 code element, and another correlator is leading-and the time-delay that postpones is 0.05 code element.In the stage of the initial captured of radiofrequency signal, used have big leading-correlator that postpones.
According to another specific target of the present invention, it is to obtain by the combination of using a specific gating signal and a totalizer/integrator that required DLL responds, rather than adopts the leading-delay version of the local PRN sign indicating number that produces.The duration of these gating signals is less than a code element, and when and the same phase time of input signal sign indicating number, will sign indicating number+produce in the saltus step between 1 and-1.Gating signal has equal positive and negative area, and has positive or negative polarity at the center, and this polarity shows that the saltus step of the PRN sign indicating number of its representative is forward or negative sense.In the process of the initial captured of radiofrequency signal, the waveform of gating signal is the pulse simple positive or that bear that produces at the sign indicating number jumping moment.
Other some targets of the present invention, the characteristics of advantage and different aspect can be found out from following its description of preferred embodiment significantly, and these descriptions should together provide with accompanying drawing.
The line-of-sight signal and the multipath signal that are received simultaneously by a GPS receiver shown in Figure 1;
Fig. 2 and shown in Figure 3 be the line-of-sight signal and the multipath signal of vector form;
Fig. 4 is total block scheme of a delay phase-locked loop (DLL) correlator;
Fig. 5 A-5D is the curve of one action of the circuit of Fig. 4;
Fig. 6 A-6C is the curve of another task of the circuit of Fig. 4;
Fig. 7 and shown in Figure 8 be the block scheme of circuit of change form of the DLL circuit of Fig. 4;
Shown in Fig. 9 A-9D is the working curve of the DLL circuit of Fig. 7 and Fig. 8;
The employing gate signal that Figure 10 has generally described another kind of type produces the correlator of local code;
Shown in Figure 11 A-11D is several modes of the circuit of operation Figure 10;
Figure 12 is an amplified version of the part of Figure 11 D;
The result that shown in Figure 13 is with the DLL correlator of three kinds of mode service charts 7,8 and 12;
Figure 14 is the block scheme that embodies a complete receiver of different characteristics of the present invention;
Figure 15 is the lower frequency changer circuit of the receiver of Figure 14, and the block scheme of timing reference circuit and sample circuit;
Figure 16 is the block scheme of a channel of the receiver of Figure 14;
The carrier number controlled oscillator that uses in each channel of the receiver of shown in Figure 17 is Figure 14;
Shown in Figure 180 is the PRN code generator of the channel of Figure 16, and their digital controlled oscillator;
Figure 19 is the block scheme of the punctual correlator that uses in the circuit of the channel of Figure 16;
Figure 20 is the block scheme of the DLL correlator (homophase and quadrature) that uses in the circuit of the channel of Figure 16; With
Shown in Figure 21 A-21D is the gate signal that replaces that possible produce in the circuit of Figure 10.
With reference to figure 1, with regard to GPS (GPS), different aspect of the present invention is described.A GPS receiver 201 includes one and is used for from the antenna 203 of satellite 207 received signals 205.From the required line-of-sight signal 205 of satellite 207 receptions, antenna 203 has also received second version of this signal, i.e. the multipath signal 209 of a delay except direct.The delay of multipath signal be because it when arriving antenna 203 the distance of process more longer than line-of-sight signal 205.Multipath signal shown in Fig. 1 is got by mountain 211 or the reflection of other object.Although the present invention only describes with a multipath signal simply as a reference, antenna 203 might receive several line-of-sight signal that postpones version simultaneously.Because GPS receiver and to be used in other other ranging receiver in using be to come work by the phase place of measuring received signal, a multipath signal will make this task greatly complicated.
In the design of antenna, done the reception that different trials limits reflected signal.Yet this is difficult, because antenna need keep the wide-angle characteristic usually, so that receive the signal that comes from several satellites that distribute quite far simultaneously.Also attempted antenna is placed in high as far as possible position, so that make the reflection of ground and buildings be kept to minimum; Or the position of carefully laying antenna makes it to avoid receiving reflected signal.Although these technology may be united employing with the present invention, the present invention has adopted different signal processing technologies to discern the multipath signal that is received in the inside of receiver.
Referring to figs. 2 and 3, the vector 213 the representative be the line-of-sight signal that is received, another vectorial 215 representatives be the multipath signal that is received.The time that multipath signal 215 arrives antenna 203 has been compared one and has postponed τ with line-of-sight signal 213.As can be seen from FIG., the intensity of comparing multipath signal with line-of-sight signal is smaller, represents with a less vector 215 among the figure.The ratio of representing these intensity here with α.
Shown in Figure 4 is general delay phase-locked loop (DLL) correlator that uses in the GPS receiver.The signal 217 that is received can be certain radiofrequency signal after amplifying of the process obtained by antenna 203, but is generally a much lower intermediate-freuqncy signal of frequency range of the signal that ratio antenna 203 received.And, in the environment of this GPS receiver, for each single composite signal by the satellite-signal of receiver antenna reception provides an independently this DLL correlator.Next each DLL correlator is handled that part of input signal from a specific satellites transmits.In addition, the signal Processing shown in Fig. 4 is finished in numeric field usually, has adopted analogue-to-digital converters with the intermediate-freuqncy signal digitizing of importing.This signal is by a sampling clock digitizing very at a high speed.
Any type of signal 217 that is received all will be in frequency mixer 219 carries out mixing with the reproducing signals 221 of the carrier wave of the signal 217 that is received.Local carrier is produced by a corresponding circuit 223, and the phase place of local carrier signal 221 is adjusted by input control signal 225.Not drawing among Fig. 4 is used for making the synchronous loop of circuit of carrier generator 223 and received signal, because this is a common design.But, but drawn out in more detail in the processing of the signal 227 of output place of frequency mixer 219, because main body of the present invention is exactly the processing procedure here.Signal 227 is the signals that received, but its carrier frequency is changed.In these two frequency mixer 229 of signal input and 231, these two frequency mixer receive the reproducing signals 228 and 230 that is carried in the PRN sign indicating number on the received signal.These reproducing signals are respectively the relation of " in advance " and " delay " on relative phase for " on time " reproducing signals 245.These reproducing signals come from a local code generator 233 in the receiver.In gps system, for the C/A sign indicating number, the sign indicating number that is carried on the received signal is known at least, and can produce in the inside of receiver.The phase place of the sign indicating number that is produced in this locality is adjusted by phase control signal 235.In addition, in some receiver, another input 237 of local code generator 233 allows the delay between the leading late replicating signal of the sign indicating number of this locality generation is adjusted.
Frequency mixer 229 and 231 output are transfused to respectively in corresponding totalizer/integrator 239 and 241.Totalizer 239 and 241 output are carried out the arithmetic addition in another frequency mixer 243, the output of frequency mixer 243 is error signals, and this error signal is input to the input 235 of local code generator 233, thereby its phase place is adjusted.Loop among Fig. 4 is to be used for the phase place of local code generator 233 is locked with the phase place that is carried in the sign indicating number on the received signal 217.Although this explanation is that the C/A sign indicating number on the L1 signal that is carried in gps satellite is provided, same principle all is suitable for many application, especially for other range finding is used.
Can help understand the work of the DLL correlator among Fig. 4 with reference to the curve of figure 5A-5D.If the punctual output 245 of local code generator 233 is acted on the totalizer of a totalizer/integrator 239 or 241 types, will produce the output characteristic curve shown in Fig. 5 A.If this punctual reproducing signals just in time with the PRN sign indicating number homophase of received signal 217, the output of so such totalizer will be in center line 247 place's maximums of the triangle output characteristic curve of Fig. 5 A.If some skew of the phase place between the two, the output of this totalizer will be delay for the PRN of received signal or move on leg-of-mutton one side or another side in advance according to local code so, to reduce from this peak value.
Although the punctual output of local code generator 233 has other purposes usually in the GPS receiver, the DLL correlator among Fig. 4 is operated the front and back version 2 28 and 230 of this yard.Shown in Fig. 5 B be and the relatively feature output of back totalizer 239 of local advanced code; And the curve of Fig. 5 C is to postpone the relatively output function of back totalizer 241 of sign indicating number with this locality.In this typical example, the leading code element that is spaced apart that postpones between the PRN sign indicating number of local generation.That is to say, postpone sign indicating number 230 and compare with anticipating signal 228 and postponed a PRN code element.This fixing delay is represented with " d " at this, and is marked in Fig. 5 B.Alternatively, as among Fig. 5 along shown in the scale of the relative phase of X-axis, the advanced code function occurs than Zao half code element of punctual version, and postpones sign indicating number than the late half code element appearance of punctual version.As shown in Fig. 5 B and 5C, can easily make the position of the output of leading and delay correlator usually for center homophase baseline 247.
Shown in Fig. 5 D is the resulting error signal 235 of correlator function that deducts Fig. 5 C from the correlator function of Fig. 5 B.When local code generator 233 during, put 247 places at homophase, consequently a null error signal just in time with the locking of the PRN sign indicating number of received signal 217.When phase place was unjustified, as known, this error signal will move along the forward or the negative sense of Fig. 5 D curve.This error signal will make the phase place of local code generator 233 move towards the direction that makes this error signal minimum, thereby make local code generator 233 and input signal keep locking.
Yet if when also having received one or more multipath signal except required line-of-sight signal, the DLL correlator of Fig. 4 will be subjected to the two influence.If when only having line-of-sight signal 213 to exist, the circuit of Fig. 4 will make it align with center zero phase reference line 247.But, because received multipath signal 215 simultaneously, and local code generator 233 " locking ' near them the imaginary signal of certain phase place, as shown in Fig. 5 D.That is to say that the Circuit lock of Fig. 4 fixes on one on the input code phase place in somewhere between the phase place of line-of-sight signal and multipath signal.Although because the decay that reflection is caused makes multipath signal compare with line-of-sight signal, intensity is lower, because the curve among Fig. 5 D is steeper, its effect can highly significant.Come together to determine the effect of multipath signal by the intensity of multipath signal with by the value of the curve at the some place of arrow 215 indications to this phase-locked operation.Line-of-sight signal vector 213 will be operated in multipath signal vector 215 homophase points 247 near.Like this because the measurement overwhelming majority that the GPS receiver is done depend on the C/A sign indicating number in the satellite-signal receiver relative phase accurately then the amount, so multipath signal this influence concerning the accuracy of final measurement highly significant.
Someone advises that in order to reduce the influence of multipath signal, the delay leading and that postpone between the sign indicating number that produces and be input in the receiver should reduce widely.Shown in Fig. 6 A-6C is effect when postponing the d=0.1 code element.Shown in Fig. 6 A is the output of leading totalizer 239 in this case.Similarly, be the output of the delay totalizer 241 of Fig. 4 shown in Fig. 6 B.Shown in Fig. 6 C is the error signal output of adder subtracter 243.Can notice that because the amplitude of error signal function reduces significantly, the influence of multipath signal 215 reduces significantly.Can from Fig. 6 C, find out error signal curve much smaller in intensity Fig. 5 B at the relative phase place of multipath signal vector 215.The result is under the stable phase locked state shown in Fig. 6 C, and line-of-sight signal vector 213 is more much closer apart from required phase-locked position 247 than line-of-sight signal.
Yet as what can see from Fig. 6 C, although the DLL correlator of Fig. 4 is worked with the leading-local PRN code phase difference of delay of 1/10th code elements, DLL still is not locked in line-of-sight signal.Error ε among Fig. 6 C is compared with among Fig. 5 D being to reduce to some extent, but do not eliminate.Multipath signal causes producing this error, and therefore reduces the precision that the GPS receiver can reach.According to characteristics of the present invention, DLL correlator by the sort of type shown in the composition diagram 7, wherein two leading-delay correlators are merged by arithmetic, and the influence of multipath signal can be eliminated in some situation, and can further be reduced in other cases.With reference to figure 7, the output 227 of carrier frequency mixing device 219 is input in two parallel correlators that connect.First correlator includes frequency mixer 251 and 253, and their output is admitted to adder subtracter 255.Then, the output of a back frequency mixer is admitted in totalizer/integrator 257.Similarly, second correlator includes frequency mixer 259 and 261, and their output is admitted to adder subtracter 263.The output of this adder subtracter is admitted to totalizer/integrator 265.
The frequency mixer 251 of first correlator receives the reproducing signals 267 of the advanced code that comes from a local code generator (not drawing among Fig. 7).Similarly, the reproducing signals 269 of frequency mixer 253 receive delay sign indicating numbers.The result is that the output 271 of totalizer has the form shown in Fig. 9 A.Delay between leading and late replicating signal 267 and 269 is set to d.This falls behind with reference to t d/2 with regulation anticipating signal 267 leading center reference phase place 279 (Fig. 9) d/2 and delay local code 269 is the same.The shape of the output shown in Fig. 9 A 271 and Fig. 6 C are similar as can be seen.
Yet, only do not rely on the output of this correlator, the local generation sign indicating number 273 and 275 of second correlator reception, differing between the leading and delay sign indicating number of these two local generations is 2d.Shown in Fig. 9 B is the output 277 of totalizer 265.Also the shape with Fig. 6 C is identical haply for the curve of Fig. 9 B as can be seen, but different with Fig. 9 A be that it has a core with long slope.This also causes the amplitude of horizontal component of curve bigger than the intensity of that part of curve of Fig. 9 A.
In another adder subtracter 283, the error signal 285 that just can obtain the form shown in Fig. 9 D is synthesized in these two outputs.This characteristic curve has very big advantage, because it has comprised that error signal is zero expansion 287 and 289.This be by with the output 271 and 277 of totalizer in frequency mixer 283 synthetic before, with a parameter 278 amplitude of the output 277 of totalizer being reduced by half, (thereby produced Fig. 9 C curve) finish.There is mathematical relation in the difference of the width of the intensity of this decay and two leading-delay correlators.In fact, in adder subtracter 283, the curve of Fig. 9 C is deducted from the curve of Fig. 9 A, thereby drawn the characteristic curve of the error signal of required Fig. 9 D.Workspace 281 is present near the homophase point 279, and wherein the circuit of Fig. 7 is adjusted the local code generator so that the error signal of Fig. 9 D is put 279 places at homophase is zero.Yet any have the signal of relative phase can not influence the synchronous of loop in zone 287 or 289.Shown in Fig. 9 D, the local code generator can be locked on the line-of-sight signal 213 under any situation about influencing of multipath signal 215 exactly not being subjected to.As long as in a code element section, the delay τ of the phase place between the vector 213 and 215 is during greater than the phase delay of workspace 281, and this just will take place.Like this, in this case, multipath signal fully has been eliminated the influence of DLL correlator.
Because the non-neutralizable fraction broad of null error signal district 287 and 289, so can compare difficulty when obtaining signal at first.That is to say, when receiver powers up first, if the relative phase of local code generator cause line-of-sight signal 213 drop on zone 287 and 289 both one of the time, used error signal when the phase place of the sign indicating number that will be not this locality not be produced is adjusted.Therefore, provide a switch 291 (Fig. 7) to be used in the process of initial signal capture, second correlator being opened from circuit interruption.Like this, in the process that sort signal obtains, the correlator output characteristic curve of Fig. 9 B does not exist, and has only the output characteristic curve of Fig. 9 A.Therefore, during this initial signal capture, multipath signal has some influences, but the purpose of this technology is that line-of-sight signal 213 is brought in the workspace 281.In case after this took place, switch 291 was closed.So just eliminated the influence of multipath signal.The DLL correlator has taken line-of-sight signal 213 to the position that overlaps fully with homophase position 279.
Say quantitatively, find when the d=0.1 code element is long, can obtain satisfied result.This means that workspace 281 is the so very narrow zone of 0.1 code element.In this example, second correlator leading-phase retardation is two times of first correlator, what wherein provide among Fig. 9 B is the output of second correlator, shown in Fig. 9 A is the output of first correlator.This makes that the duration of each null error signal district 287 and 289 is 0.8 code element, can getable relative differences 80% be between the PRN of local code and received signal sign indicating number.
In the concrete parameter in the correlator of Fig. 7 and Fig. 9 many variablees are arranged, can select to control the work of this correlator these variablees.Be two correlators selected specific leading-postponing to differ can be within a big scope, as long as they are different, this phase extent depends on certain specific application and the requirement that will reach.But one of two correlators that usually preferably make Fig. 7 have one to be ahead of the leading PRN sign indicating number of homophase latched position t1/2k and its delay PRN sign indicating number of 1/2k after t.Similarly, second correlator has the leading PRN sign indicating number of a leading tN/2k phase place and the delay PRN sign indicating number of a hysteresis tN/2k phase place.N and k are integer, and wherein N is less than k.In the example of being given, N=2 and k=10.If follow these restrictive conditions, the scale factor of the parameter 278 of Fig. 7 will remain 1/2.If between two correlators, have some other relation, expand null error signal district 287 and 289 in order after from the totalizer output of Fig. 9 A, the totalizer output of Fig. 9 C being deducted, to produce so, scale factor will be different.
One of shown in Figure 8 is among Fig. 7 circuit is improved circuit, wherein uses four totalizers to replace two totalizers 257 and 265 among Fig. 7.The purpose of Fig. 8 is to be used for showing if to frequency mixer 251,253, and 259 and 261 do anyly these outputs to be added up respectively and will obtain identical result before synthetic.Adder subtracter 293 will receive the output of these four totalizers then, and two needs in these outputs this moment are scaled and be switched, and have only an output 277 need carry out these operations among Fig. 7.
Being to use in advance shown in Figure 10-postpone the another kind of method of correlator, but this method can provide same useful results.The same described in Fig. 4,7 and 8 as the front, a signal that is received 301 is admitted to frequency mixer 303, and this frequency mixer also receives the reproducing signals 305 that is included in the carrier wave in the signal 301 simultaneously.Have the signal 307 that is removed a local carrier and in frequency mixer 339, carry out mixing with the strobe pulse sequence 341 that comes from local strobe generator 343.Output signal after the mixing of frequency mixer 339 is admitted in totalizer/integrator 345, and the output 347 of this totalizer/integrator is the phase error signal that is used to adjust the output of local this signal generator 343, so that this error signal minimum.
Can explain the work of the DLL correlator of Figure 10 with reference to the curve of Figure 11.Shown in Figure 11 A is that a part as received signal 301 is modulated onto the PRN sign indicating number on the carrier wave.This sign indicating number is binary, or is+1 level, or is-1 level.One of them of these level represented binary digit 1, and another represents binary digit zero.Saltus step between these level occurs in a symbol interval place.Yet the level of this sign indicating number be not each code element with regard to saltus step once, its information spinner will be included in the pseudo-random fashion, in this kind mode, in one or several code element is a value, switch to another value in one or several code element under connecing then, and then return, so go down.
Shown in Figure 11 B is a kind of strobe sequence 341 that can be used, and when each positive transition of the input code of Figure 11 A, the value of this sequence is+1, and when each negative sense saltus step of input code, the value of this sequence is-1 simultaneously.When not having saltus step, this situation is possible, and strobe sequence 341 is zero (Figure 11 B).The saltus step of the strobe sequence of Figure 11 B takes place at the middle of code element of each input code.Using the result of the strobe sequence of Figure 11 B is an error signal 347, and this error signal is the same with the effect of the error signal shown in Fig. 5 D in essence.Just when the strobe sequence 341 of the DLL of Figure 10 correlator is shown in Figure 11 B, the resulting result of this correlator in fact with Fig. 4 in the local leading-result that postpones the DLL correlator gained of PRN sign indicating number who separates by a code element who produces of employing be the same.
Shown in Figure 11 C is a strobe sequence 341, and the error signal 347 that this sequence provides is substantially the same with the error signal shown in Fig. 6 C.The pulse that pulsewidth is 0.1 code element produces simultaneously in saltus step place of the input code of each 11A.When input code was positive transition, the polarity of this pulse was for just; When input code during for negative saltus step, the polarity of this pulse is for negative.The width of this pulse can not be 0.1 code element, will obtain an error signal function different with the error signal function shown in Fig. 6 C so.
Shown in Figure 11 D is designed local strobe sequence of characteristics according to the present invention.Use the resulting error signal 347 of strobe sequence 341 (Figure 10) of this form have basically with Fig. 9 D in the same effect of error signal.In order to achieve this end, the appearance of each saltus step of the input code of this strobe sequence and Figure 11 A produces simultaneously, and include one have simultaneously on the occasion of with the pulse of negative value.Door sequence 341 is zero between two this impulse functions.The duration of these impulse functions is much smaller than a code element.Each impulse function has equal positive and negative area.When phase-locking realizes, the core of the impulse function of Figure 11 D will align with the trip point of the input code of Figure 11 A.If this saltus step is a forward, the polarity of the core of the impulse function of Figure 11 D is a kind of polarity so; If the input code saltus step is a negative sense, the core of this impulse function just has opposite polarity so.In Figure 11 D, constantly 349 with the produced simultaneously core in positive transition edge of the input code of Figure 11 A be positive polarity, and constantly 351 with the produced simultaneously core in negative sense saltus step edge of the input code of Figure 11 A be negative polarity; But these polarity also can be conversely.
With reference to Figure 12, the feature of the impulse function of Figure 11 D will describe in the figure of this up-sizing.The single impulse function that is occurred around input code saltus step 349 can be seen as four different adjacent parts.The core of impulse function has zone 353 and 355, and when the error signal of the correlator of Figure 10 reaches hour, the area in this two zones on the relative both sides of saltus step line 349 equates.The polarity in zone 357 and 359 is opposite with zone 353 and 355, and they appear at the front and back in impulse function zone 353 and 355 respectively.353 and 357 area is equated.Similarly, 355 and 359 area is equated.In described concrete example, the wide of zone 353 and 355 is 0.1 code element, and amplitude is+1; And the zone 357 and 359 wide for the zone 353 and 355 width 1/2 or be 0.05 code element, amplitude is-1.
With reference to Figure 13, the curve of being given is the relative tracking error border of the different multipath signal of explanation, and wherein these different multipath signals have different length of delays to the line-of-sight signal of required locking.Shown in the outer curve 361 and 363 is the result of the DLL correlator of Fig. 4 with the mode work of the curve among Fig. 5.Shown in the dot-and- dash line 365 and 367 is the working condition of the DLL correlator of Fig. 4 with the curve of Fig. 6, as described above.Can see that it is a lot of that tracking error reduces, but still clearly.Shown in the curve 369 of Figure 13 is that illustrated as the curve among Fig. 9, how this error is significantly reduced when a DLL correlator in Fig. 7 or 8 is used.As the said mistake in front, when adopting the strobe sequence of Figure 11 D in the correlator at Figure 10, will obtain and identical result shown in the curve 369.Can notice from curve 369 with line-of-sight signal has the multipath signal of bigger delay that tracking is had no effect.
More particularly, Figure 13 postpones the envelope of the zero tracking error that concerns between the τ to have shown the ε that represents three DLL correlators and nanosecond nanosecond (ns), wherein the ratio cc of the amplitude of the amplitude of multipath signal and line-of-sight signal is 0.5, θ-π and+change between the π.Clearly, for 0 and 10ns between τ for, the zero tracking error of three correlators almost is desirable.For near the τ the 100ns, the edge DLL of 0.1 code element has remarkable advantages.After 150ns, the zero tracking error of the edge correlator of d=0.1 code element becomes very little; And this error of arrowband correlator rests on 30ns; The zero tracking error of the wide correlator of 1 code element is greater than 30ns and constantly increase at this moment.Conceptive, the C/A sign indicating number is used edge DLL correlator and uses the DLL correlator to be equal to the P sign indicating number, and have the characteristic that same favourable multipath alleviates.
The following description mainly is the GPS (GPS) at the U.S.; But it also is applicable to the GLONASS (Global Navigation Satellite System) (GLONASS) of the Commonwealth of Independent States (CIS), and the range measurement system of any employing PRN sequence.Present embodiment is described with a bit quantization; The purpose of doing like this is for explanation being oversimplified, not got rid of any relevant restriction that quantizes.
With reference to Figure 14, this figure is a whole block scheme of realizing a pseudo noise of the present invention (PRN) receiver 10.Receiver 10 includes 11, one low-converters 12 of an antenna, and a plurality of channel 13a are to 13n, an input/output interface 14 and a digital processing unit 15.Antenna 11 receives a composite signal RF, and signal RF is made up of the signal that all come from the satellite in this system within the sighting distance of antenna just in time.Composite signal RF is admitted in the low-converter 12, quantizes sampling intermediate-freuqncy signal IFW, a system sampling clock Ft and a system clock to produce one.
Signal IFW is one 4 a word, in four adjacent IF sample values that each representative is adopted with the Fs sampling rate one.Work clock Ft obtains the Fs signal divided by 4.System clock is the further frequency division of Ft signal, system clock with near every millisecond once the speed interrupt handler and trigger the operation of channel.
With reference to Figure 15, what describe among the figure is low-converter.The RF signal is at first by 120 pre-filterings of RF wave filter, amplified by 121, carries out mixing with local oscillator (L0) then in frequency mixer 122, and in IF by 123 and 124 filtering and amplifications, last hard limiter 125 carries out the quantification of a bit to it.In fact wave filter 123 is used as the pre-correlation filter that a bilateral bandwidth is 20.46MHz.Sample frequency with Fs is sampled to the instantaneous output of hard limiter, and with among its shift-in level Four shift register 126.Sample frequency Fs selects according to the bandwidth of pre-correlation filter, satisfy the requirement of Nyquist sampling frequency.Each Ft clock saltus step (4 Fs clocks just), the full content in the shift register will be sent in the parallel register 127.This 4 bit words IFW will be admitted in the channel circuit with the speed of Ft and be used for satellite is followed the tracks of separately then.
The clock reference circuit of low-converter (Figure 15) includes a phaselocked loop (PLL), it carries voltage controlled oscillator (VCO) 131,132, one of frequency divider is used for phase comparator 129 and a low frequency loop filter 130 that phase place is compared with a stable reference oscillator 128.The output of VCO wherein is used as the local oscillator of RF part.The frequency of VCO131 divides several steps by frequency division, at first with frequency divider 133 to its frequency division to obtain sample frequency Fs, next obtain work clock Ft with frequency divider 134, obtain system clock with frequency divider 135 at last.
As shown in Figure 14, the intermediate-freuqncy signal IFW behind sample quantization is admitted to several signal processing channels 13a simultaneously in 13n.One independently channel 13 be exclusively used in each visible satellite; By the order of PRN generator pseudo noise (PRN) generator is provided with, channel allocation is given the satellite of an appointment.Channel 13 is that each normal structure of channel 13a-13n provides in Figure 16.Utilize a carrier phase-locked loop (PLL) that each satellite-signal is traced on the carrier phase, utilize a delay phase-locked loop (DLL) that each satellite-signal is traced on the code phase simultaneously.The processing of all channels is all carried out in complete synchronous mode with work clock Ft.The IFW sample value is per 4 handles together that all carrier waves and code also are with 4 one group generation of Ft frequency simultaneously.
PLL and DLL part realize that in channel 13 part realizes in processor 15.The connection of signal is finished by I/O interface 14.Loop comparer and loop driver are all arranged, although the management of the realization of wave filter and loop is finished by processor 15 in each channel.When processor is interrupted by system clock, simultaneously for channel is provided with when measuring ready signal, this signalisation processor finishes a measuring period, and loop will be updated.All be chosen to be greater than system clock cycle all measuring periods, so that do not lose any measurement.This cycle is instructed by the PRN generator by processor in each channel initialization and is provided with.
Carrier wave PLL utilizes measurement result I and the Q of homophase correlator 130a and quadrature phase correlator 130b.Under tracing mode, the signal that the PLL check occurs is when being locked on the I, with information Q vanishing.Two correlators use identical " on time " pseudo-random code (PRN) to be correlated with, but use different carrier signal COS and SIN.The information of handling is used to control the carrier frequency instruction of numerical control carrier oscillator (NCO) 132.
Figure 17 describes in detail carrier wave NCO132.Instantaneous carrier phase figure is stored in the carrier phase register 1325, and wherein to represent the phase place of carrier wave be 2 π to full scale.Current carrier frequency instruction is stored in the frequency instruction register 1323.During each Ft saltus step, this value is added in the current carrier phase register by totalizer 1321C; Each like this when phase register 1325 loops back zero, the phase place of carrier wave will increase by a complete cycle.
This instantaneous carrier phase place can very directly obtain in any system clock saltus step place or at each Ft place.When initial channel reset instruction, carrier phase register 1325 is synchronously resetted, to guarantee a known initial phase with system clock.Each processor instruction that is loaded in the buffer 1324 all is admitted in the frequency instruction register 1323, and works when next system clock saltus step; Because system clock cycle is the definite numerical value in a Ft cycle, also known the instruction word that is loaded simultaneously, so the definite value in the carrier phase register can be by directly calculating in the middle of system clock saltus step next time or any Ft clock saltus step.
The cosine value Co of the reference carrier of one bit carries out XOR by the highest significant position (MSB) with the carrier phase content of registers with second highest significant position to obtain.The sine value of the reference carrier of one bit is to obtain because of the highest significant position of this carrier phase register (MSB); This is actually finishes in phase place/orthogonal signal generator 1320C.
Because sample value be per 4 processing once, so carrier reference signal also will produce synchronously in the accurate sampling instant of other 3 sample values.Artificially and in order to realize for simplicity, reference signal is chosen as the 3rd sample value of the sequence that these 4 sample values form.
Can notice that the in fact every Ft of carrier phase 1325 increases once by frequency instruction value 1323.Also can say so, the every Fs of this instantaneous carrier phase increases (be every Ft cycle four times) with this value of 1/4th.Therefore, the phase place with the synchronous reference carrier of the 4th sample value (nearest) is to be added to by the frequency instruction after will being removed by four (divider 1322C) to obtain on the current carrier phase 1325; Cosine (sine) the value C that has postponed the carrier wave in a sampling period + 1(S + 1) be to adopt and ask Co and the same algorithm of So, obtain from the above reference carrier phase place that obtains with quadrature in phase signal generator 1320d.
Similarly, C -2, S -2By from current carrier phase 1325, deducting frequency instruction value is obtained divided by the resulting value in 2 backs with 1322a.This operation of subtracting each other is finished by totalizer 1321a.These two cosine and sine value are finally obtained by 1320a.
At last, C -1, S -1By from current carrier phase 1325, deducting frequency instruction value is obtained divided by the resulting value in 4 backs with 1322b.This operation of subtracting each other is finished by totalizer 1321b.These two cosine and sine value are finally obtained by 1320b.
Complete NCO output is made up of " sine " word SIN of four " cosine " word COS and four, and every is the reference value of the carrier wave after the sampling of a sample value apart.Described in Figure 19 is " on time " homophase (130a) and quadrature phase (130b) correlator that is used for phaselocked loop (PLL).Because these two kinds of correlators are very similar, below the description of relevant correlator only be directed to the situation of homophase.
The intermediate frequency word IFW that forms by 4 sample values in member 1301a to 1301d with the carrier wave of 4 cosine with reference to COS XOR mutually.The addition in totalizer 1302 of all sample values; The result-4 and+4 between (totalizer 1302 is handled " 0 " value as " 1 ").Then, this result with and the nearest value of the synchronous reference PRN sequence of sample value multiply each other (multiplier 1303).This end value then with the Ft frequency by algebraically be added in the current content of totalizer 1305.During each cycle saltus step, the value in the totalizer is imported in the buffer, and totalizer is reset, and begin last new measuring period.At this moment processor just can read this measured value to finish this loop.
Temporarily get back to Figure 16, will be described in greater detail delay phase-locked loop.This DLL has two kinds of configurations, and acquisition mode or tracing mode depend on the phase place of channel locks to the selection of these two kinds of patterns.As described in the part in front, tracing mode preferably adopts " edge DLL " correlator, and acquisition mode preferably adopts 0.1 symbol delay DLL.Selection between two kinds of patterns selects signal to finish by DLL.Also can use the combination of other specific tracking and acquisition mode correlator.
Similar with PLL, the processing procedure of delay phase-locked loop (DLL) is carried out with the Ft frequency, and its measurement renewal frequency also is CYCLE simultaneously.This DLL uses dI and dQ information, and wherein dI comes from homophase DLL correlator 131a, and dQ comes from quadrature phase DLL correlator 131b.When in tracing mode, this DLL will the value of making dQ vanishing.When at acquisition mode, dQ will be used together with dI.Information after the processing is used to control the PRN generator instruction of PRN code generator 133.
The front is according to Figure 10, and the principle of 11D and 12 described " edge DLL " will be carried out more detailed explanation to it by described GPS receiver just now.In order to realize the intention of " edge DLL ", must around the saltus step of PRN sign indicating number, define the time interval that four width equate, two before the sign indicating number saltus step, two after the sign indicating number saltus step.In current embodiment, each time interval has the width in same 1/FS or IF sampling period.
We therefore know by inference each time interval include one and have only one with frequency Fs adopt the IF sample value.The relative position of sample value is ignorant in the interval, and this relative position depends on the relative phase between code generator and the sampling clock.To provide the expressed intact formula of DLL response below.
Suppose S -2, S -1, S + 1, S + 2Be a sequence of being made up of four adjacent IF sample values, wherein the sign indicating number saltus step is at S -1And S + 1Between, the PRN sign indicating number sequence after the Xiang Guan sampling is PRN simultaneously -2, PRN -1, PRN + 1, PRN + 2(PRN wherein -2=PRN -1, PRN + 1=PRN + 2).DPRN can be defined as:
DPRN=1/2 (PRN + 1-PRN -1) like this dPRN equal:
+ 1, if saltus step is a rising edge
-1, if saltus step is a negative edge
0, if two continuous PRN code elements are identical.DPRN can be counted as the difference quotient of PRN sequence.
During each PRN sign indicating number saltus step, basic DLL effect is provided by following formula:
DLLi=(S -2+ S -1+ S + 1-S + 2) if dPRN dPRN ≠ 0 (is PRN -1≠ PRN + 1), then should be worth non-vanishing.
After an integration period, this integration period is defined as two times between the adjacent CYCLE saltus step, total DLL response will for:
DLL=∑ DLLi should sue for peace measured value dI and dQ had been made low-pass filtering one time.
Get back in the actual implementation, though we notice that we know that a yard saltus step drops between one group of four IFW sample value, we need know also still this yard saltus step drops between which two sample value of this group.Signal P 0And P 1Where middle show that the sign indicating number saltus step drops on 4 IFW sample values.Because we need be with 4 adjacent value additions, the sign indicating number saltus step has 4 different positions in this sequence simultaneously, so we need keep three sample values of 4 IFW sequences of front.Whole sequence will for, arrange from the oldest sample value to up-to-date sample value: S 2A, S 3A, S 4A, S 1, S 2, S 3, S 4And PRN 4, PRN 4Be and S 4Synchronous PRN sign indicating number.
Table 1
?P 1Value P 0Value The sign indicating number saltus step drops on Basic DLL work in the tracing mode Basic DLL work in the acquisition mode
?0 ?0 S 3AAnd S 4A (-S 2A+S 3A+S 4A-S 1)dPRN (+S 2A+S 3A+S 4A+S ?? 1)dPRN
?0 ?1 S 4AAnd S 1 (-S 3A+S 4A+S 1-S 2)dPRN (+S 3A+S 4A+S 1+S 2) ????dPRN
?1 ?0 S 1And S 2 (-S 4A+S 1+S 2-S 3)dPRN (+S 4A+S 1+S 2+S 3) ????dPRN
1 ?1 ?S 2And S 3 (-S 1+S2+S 3-S 4)dPRN (+S 1+S 2+S 3+S 4) ????dPRN
Referring to Figure 20, described the realization of homophase DLL correlator 131a among the figure in detail.After IFW being multiplied by carrier wave word COS with 1310a to 1310d, last three sample values of current I FW word are latched in 1318.At the input end of four multiplexer 1311a, can obtain 7 sample values simultaneously, S to 1311d 1To S 4Come from current I FW, and S 2ATo S 4ACome from previous IFW.According to P 1And P 0Value all 4 multichannels modulation systems are selected jointly.In the following description, we will suppose P 0=P 1=0.Output terminal at 1311a will obtain S 1Output terminal at 1311b will obtain S 4A, or the like.Totalizer 1313 is with all sample value additions of selecting (in this process, regarding " 0 " input as value " 1 ").Next this result will multiply each other with dPRN, thereby obtain basic value DLLi.Under tracing mode, signal DLL selects to make from first value reversion with last multiplexer output, has so just fully realized the described tracking DLL formula of first row at table 1.
With in the process of a Ft saltus step, by totalizer 1315, the currency between+4 and-4 by algebraically be added in the totalizer 1316.The every saltus step of CYCLE once, the value in the totalizer just is introduced in the buffer 1317, and totalizer is resetted, and triggers a new measuring period at last.
When realizing acquisition mode, have only some difference.Circuit up to totalizer 1313 is the same, just from first and last sample value reversion not of multiplexer 1311a and 1311d output.The dPPN signal defines in the identical mode in front, but its duration extend to 0.1 code element, be centered close to the sign indicating number trip point.
With reference to Figure 18, will complete PRN code generator be described.In fact this generator is made up of a code digital controlled oscillator (NCO), and this oscillator sends code frequency clock Fc, and the frequency of this clock is directly controlled by processor by the code frequency instruction; Fc itself is again as the clock of PRN code generator 1334.
Let us is from the description of sign indicating number NCO: NCO is similar with carrier wave, and it realizes that by a code phase register 1335 full scale of this register is represented the code phase of 2 π.During each Ft saltus step, totalizer 1331d is added to the word in the code frequency order register 1336 in the content of (with the range delivery of code phase register) code phase register.Carry signal from totalizer 1331d is used as code frequency Fc.The code frequency instruction that occurs in the code frequency order register is to pack into from buffer 1337 in the moment of each system clock saltus step.This impact damper itself is at any time from the processor loading instruction.The Another important function of sign indicating number NCO is to be used for sending signal P 0And P 1, the effect of these two signals was described in front.
P 0And P 1Signal is to produce according to following regulation: if R is total range of code phase register (CPR) 1335, Δ is the increment (Δ =code frequency instruction/4) of the phase place of every Fs sampling sample value.
Table 2
0＜CPR≤Δ 0＜CPR≤2Δ ?2Δ＜CPR≤ ????R-2Δ ?R-2Δ＜CPR≤ ????R-Δ ?R-Δ＜CPR≤R
?P 1 ????0 ????0 ????1 ????1 ????1
?P 0 ????1 ????0 ????0 ????1 ????0
P 1Be to obtain after divided by 2 later code frequency registers (CFR) 1336 by using totalizer 1331c from code phase register (CPR) 1335, to deduct (by divider 1332b).If RES1 is on the occasion of, P then as a result 1=1.
P 0Situation according to different P 1The value and different.If P 1Be zero (CPR＜2 Δ ), CFR is removed back (using divider 1332a) by 4 and multiplies each other with-1 in multiplier 1331b; If P 1Be 1 (CPR 〉=2 Δ ), CFR/4 will with+1 multiply each other.Then, 1331a is added to RES1 on the multiplied result, and the carry of totalizer 1331a is as P 0Last result is consistent with table 2.
The clock of PRN code generator 1334 is code frequency Fc.It is to be used for that reset instruction produces a special satellite sequence according to generator.Synchronous epoch signal of special occasion in one of its output and the PRN sequence, this signal are used as find range reference signal in the sequence of PRN.The saltus step and this epoch signal that are superimposed upon the data bit on the PRN sequence are synchronous fully.
This epoch signal is as the clock of cycle counter 1333, this counter is made it to reset by synchronous reset signal in channel initialization, and before the saltus step that produces on the CYCLE, calculate the integer number (resetting at homing sequence) of epoch, this operation will stop current measuring period on all correlators sends and measures the ready signal notification processor.Each channel all has the synchronous cycle counter of the saltus step with its data of oneself.When with the saltus step homophase of data after, may be dropped to 20ms measuring period, in this period, do not have the saltus step of data to take place.
Suppose to determine that the edge DLL that is used for the C/A sign indicating number that has pre-correlated bandwidth pre-filtering (being generally the 20.46MHz double-side band) has improved the multipath mistake.PRN sign indicating number transition detection device is latched in yard mutually XOR in the latch 1339 with current sign indicating number output and front.Signal dPRN produces by 1338 according to the description in the explanation of DLL principle.
According to common multipath model, direct received signal is to be given by the following formula:
APRN (t) cos (ω 0T+ ) wherein
A is the amplitude of the signal that received
PRN (t) is a pseudo-random sequence
ω 0It is the angular frequency of carrier wave
is the skew of carrier phase,
Multipath signal is given by the following formula:
A·α·PRN(t-τ)·cos(ω 0(t-τ)+-θ)
Wherein:
α is the ratio of the amplitude of direct signal and multipath signal;
τ is the propagation delay between direct signal and multipath signal;
θ is phase place rotation additional between direct signal and the multipath signal.
The main influence that multipath signal exists is that the zero crossing that makes the DLL of three phase detectors response has departed from " zero multipath " reference point respectively, and the distance of skew has nothing in common with each other.It is zero that DLL makes the mean value of the output of DLL correlator, and the difference between the zero crossing will directly be regarded as the error of the code phase that records.Because different satellites is had different geographical situations, these channels do not have identical multipath signal, so the calculating in orientation has error.
Get back to the front about relevant Figure 11 D of the work of the receiver of the demodulation techniques of use Figure 10 and 12 explanation, will describe several local strobe sequence that replace.Figure 21 B, 21C has provided which information relevant gate signal generator 343 can provide in sequence 341 other examples with 21D.The feature of the error signal that is drawn is the same with Fig. 9 D substantially, but the different strobe sequence among Figure 21 B-D will make height and some variation of duration of non-null part in Fig. 9 D curve.Wherein basic advantage has been retained, and the error signal that extended is provided is time interval of zero.
In every width of cloth figure of Figure 21 B-D,, produced the gating signal of meticulous control in saltus step place 365,367 of each input code (Figure 21 A) or the like.In Figure 21 B, the negative loop 369 of signal and 371 amplitude are less than 1, and the corresponding amplitude on the occasion of part 373 and 375 is 1.Yet the amplitude of the negative loop of signal is more little, and the time that it continued is just long more, so just makes the area of pulse burst 369 and 373 equate that 317 and 375 area also equates simultaneously.In the gating signal of Figure 21 C, positive area 377 (amplitude is less than 1) is more much smaller than negative long-pending 379 (amplitude is greater than 1), and positive area 381 is more much bigger than negative sense area 383.This gating signal is different with other gating signal of being showed here is to align with the negative saltus step of moving towards part and just moving towards between the part of edge 365 (when the having the least error condition) signal of sign indicating number.Figure 11 D, 12, each signal is about the edge symmetry of sign indicating number among 21B and the 21C.The center of signal and sign indicating number justified margin.
Yet the gating signal among Figure 21 D is not about input code edge symmetry.But it is identical with the negative area that moves towards pulse burst at the area of the pulse burst that is just moving towards on each limit at sign indicating number edge.That is to say that the area 385 and 387 on the one side at sign indicating number edge 365 equates substantially, and also equate substantially at the area 389 and 391 of the another side at sign indicating number edge 365.
Although provided the concrete example of several compound strobe pulse shapes, also have many other shapes to be used with different relative amplitudes.Any this compound strobe pulse total negative moves towards area and just moves towards area and be designed to about equally.This specific character makes when as long as the delay between multipath signal and the line-of-sight signal is enough, and multipath signal will be eliminated substantially.
Although different aspect of the present invention is illustrated in their preferred implementation, the present invention is protected in the gamut of appending claims.

Claims (25)

1. one kind to including the method for the input signal decoding of adopting the carrier wave that pseudo noise (PRN) binary code encrypts, comprising:
At the PRN signal of this locality generation corresponding to the PRN sign indicating number of input signal,
With the PRN signal and the input signal mixing of this locality generation,
The PRN signal that produces from this locality and the result of input signal mixing have produced an error signal, the amplitude of this error signal is the PRN sign indicating number of input signal and the function of the relative differences between the local PRN signal that produces, this funtcional relationship is a) for the most relative differences in the scope between zero relative mistake and the positive and negative code element, this amplitude is 0, b simultaneously) when this relative differences during from another value that zero changes to the core of above-mentioned scope, this amplitude will increase, and
When being the amplitude of non-zero in the above-mentioned core of error signal in above-mentioned scope, the method of adjusting above-mentioned relative differences by the phase place of adjusting the local PRN signal that produces makes the error signal vanishing, thereby makes relative differences vanishing between input signal PRN sign indicating number and the local PRN signal that produces.
2. the method for claim 1, this locality of wherein corresponding with the PRN sign indicating number of input signal PRN signal produces a computing collection of the gating signal of the non-zero that comprises the PRN sign indicating number edge that produces the representative input signal that repeats, and these gating signals are distinguished (a) lasting time less than a code element, (b) equal forward and negative sense area are arranged, and (c) have the corresponding positive or negative polarity of moving towards with the plus or minus at PRN sign indicating number edge at the center.
3. according to the method for claim 2, wherein before this locality produces the computing collection of above-mentioned gating signal, produce an initialization collection of the gating signal that repeats of non-zero, and these gating signals respectively all (i) lasting time less than a code element, and have (ii) that to represent a PRN sign indicating number edge respectively be just to move towards or the single positive polarity or the negative polarity of negative trend, thereby produce in this locality before the computing collection of gating signal, when beginning, catch an input signal.
4. according to the method for claim 1, this locality of wherein corresponding with the PRN sign indicating number of input signal PRN signal produces the computing collection that comprises a PRN signal, first reproducing signals is for the 1/2k of a reference signal leading above-mentioned code element on phase place, second reproducing signals falls behind the 1/2k of above-mentioned code element on phase place for above-mentioned reference signal, the 3rd reproducing signals is for the N/2k of above-mentioned reference signal leading described code element on phase place, with the N/2k of the 4th reproducing signals for described reference signal backward above-mentioned code element on phase place, wherein N and k are integers, and N is less than k.
5. according to the method for claim 4, wherein the reproducing signals mixing of input signal and the first, second, third, fourth local PRN sign indicating number that produces has been produced the signal after the corresponding first, second, third and the 4th mixing, and the process that wherein produces error signal comprise give first with the 4th mixing after signal same but the polarity different with the common polarity of the second and the 3rd signal.
6. the method for claim 4, wherein k equals 10, and N equals 2.
7. the method for claim 4, wherein before this locality produces the computing collection of PRN signal, generation includes the first and second above-mentioned reproducing signals, and do not comprise the initialization collection of the PRN signal of third and fourth reproducing signals, thereby produce in this locality before the computing collection of gating signal, when beginning, catch an input signal.
8. any one method in the claim 1 to 7, wherein input signal comprises main signal and multipath version that the main signal that is received of phase delay is arranged from transmitter that at least one is directly received in sighting distance, this phase delay is greater than the center section of above-mentioned error signal scope, therefore the adjustment of relative differences is only relevant with this main signal, and irrelevant with multipath signal.
9. in a kind of receiver of the radiofrequency signal that includes the carrier wave of being encrypted by pseudo noise (PRN) binary code, when also having received the multipath version that postpones from the part symbol time of having of the main signal in sighting distance of transmitter that is received, method on a kind of PRN sign indicating number that locks onto this signal comprises:
Generation is corresponding to the PRN signal of the PRN sign indicating number of received signal,
PRN signal that produces and the signal that includes main signal and its delay multipath version that is received are carried out mixing,
According to an error signal, adjust the PRN signal produced relative phase and
During beginning the phase place of the PRN signal that produces compared with the phase place of the reset signal of main signal and multipath signal and produce error signal, next comparing with the phase place of the main signal that does not have multipath signal from the phase place of the PRN signal that will be produced then produces error signal.
10. the method for claim 9, wherein the generation of PRN signal comprises a computing collection of the non-zero gating signal that produces the representative PRN sign indicating number edge that repeats, and these gating signals lasting time in when beginning (i) less than a code element, and have (ii) that to represent a PRN sign indicating number edge respectively be just to move towards or the single positive polarity or the negative polarity of negative trend, then next (a) lasting time is less than a code element, (b) equal forward and negative sense area are arranged, and (c) have the corresponding positive or negative polarity of moving towards with the plus or minus at PRN sign indicating number edge at the center.
11. method according to claim 9, wherein the generation of PRN signal comprises at first and to produce than first reproducing signals of the N/2k of the leading above-mentioned code element of phase place of a reference signal with than second reproducing signals of the N/2k of the above-mentioned code element of phase lag of above-mentioned reference signal, next add then than the 3rd reproducing signals of the 1/2k of the leading above-mentioned code element of phase place of above-mentioned reference signal with than the 4th reproducing signals of the 1/2k of the above-mentioned code element of phase lag of above-mentioned reference signal, wherein N and k are integers, and N is less than k.
12. the method for claim 11, wherein k equals 10, and N equals 2.
13. one kind to including by the puppet method of the input signal decoding of the carrier wave encrypted of noise (PRN) binary code with the letter, comprising:
Produce the non-zero work gating signal at the representative PRN sign indicating number edge that repeats in this locality, and this signal respectively (a) lasting time less than a code element, (b) equal forward and negative sense area are arranged, and (c) has the corresponding positive or negative polarity of moving towards with the plus or minus at PRN sign indicating number edge at the center
Input signal and each are carried out mixing in the gating signal of this locality generation, thereby produce first and second mixed frequency signals,
The first and second above-mentioned mixed frequency signals are correlated with and are added up, thereby obtain a coherent signal, and
Use coherent signal to adjust the phase place of the local gating signal that produces according to the PRN sign indicating number of input signal, so that this correlation maximum, thereby on the phase place of the PRN sign indicating number of the phase locking of the gating signal that this locality is produced in the input signal.
14. method according to claim 13, wherein before this locality produces above-mentioned work gating signal, generation has the initial gating signal of the non-zero gating signal that repeats, these signals separately (i) lasting time less than a code element with have (ii) that to represent a PRN sign indicating number edge be just to move towards or the single positive polarity or the negative polarity of negative trend.
15. according to the method for claim 13, wherein each gating signal has the identical duration that the part with a code element of the PRN sign indicating number of input signal is represented.
16. the method that the input signal that includes the carrier wave of being encrypted by pseudo noise (PRN) binary code is decoded comprises:
Produce the reproducing signals of input signal PRN sign indicating number in this locality, this reproducing signals includes first reproducing signals than the 1/2k of the leading above-mentioned code element of phase place of a reference signal, second reproducing signals than the 1/2k of the above-mentioned code element of phase lag of above-mentioned reference signal, the 3rd reproducing signals than the N/2k of the leading above-mentioned code element of phase place of above-mentioned reference signal, with the 4th reproducing signals than the N/2k of the above-mentioned code element of phase lag of above-mentioned reference signal, wherein N and k are integer, and N is less than K
The reproducing signals of input signal and the local PRN sign indicating number that produces is carried out mixing,
Signal after the mixing of the reproducing signals of input signal and PRN sign indicating number is synthetic and add up, thus a coherent signal obtained, and
Use coherent signal to adjust the phase place of the local gating signal that produces according to the PRN sign indicating number of input signal, so that this correlation maximum, thereby on the phase place of the PRN sign indicating number of the phase locking of the gating signal that this locality is produced in the input signal.
17. the method for claim 16, wherein K equals 10, and N equals 2.
18. the method for claim 16 is wherein carried out mixing with first, second, third, fourth reproducing signals of input signal and the local PRN sign indicating number that produces and is obtained corresponding first, second, third, fourth mixed frequency signal; And wherein give first identical with the 4th mixed frequency signal and opposite with the common polarity of second and second mixed frequency signal polarity synthetic comprising with the process that adds up with above-mentioned mixed frequency signal.
19. the method for claim 18, wherein the process synthetic and that add up of above-mentioned mixed frequency signal is to add up earlier, synthesizes then.
20. the method for claim 18, wherein the process synthetic and that add up of above-mentioned mixed frequency signal is to carry out some at least earlier to synthesize before adding up.
21. the receiver of a compound radio-frequency signal, wherein this compound radio-frequency signal includes a plurality of signals, and in these signals each all comprises and comprises a radiofrequency signal of being encrypted by pseudo noise (PRN) binary code:
Receive this compound radio-frequency signal and convert this composite signal the device of an intermediate-freuqncy signal to, thereby this intermediate-freuqncy signal has comprised a plurality of signals, and in these signals each all comprises one by the intercarrier signal of PRN code encryption,
The channel circuit of a plurality of these intermediate-freuqncy signals of reception, each in above-mentioned a plurality of channel circuits all includes one of them device of decoding that is used for these a plurality of intermediate-freuqncy signals, and this device comprises:
To the error signal devices sensitive, this device is used at PRN the sign indicating number corresponding and PRN signal that relative phase by the amplitude of error signal controlled of this locality generation with intermediate-freuqncy signal,
Be used for the device that PRN signal that this locality is produced and intermediate-freuqncy signal carry out mixing,
Use this mixed frequency signal to produce the device of error signal, the amplitude of this error signal is one the PRN sign indicating number in those intermediate-freuqncy signals and the function of the relative differences between the local PRN signal that produces, this funtcional relationship is that (a) is for the most relative differences in the scope between zero relative differences and the positive and negative code element, this amplitude is zero, simultaneously (b) when this relative differences when zero changes to another value of core of above-mentioned scope, this amplitude will increase.
22. the receiver of claim 21, wherein local PRN signal generation apparatus comprises the device of a computing collection of the non-zero gating signal that is used for producing the representative PRN sign indicating number edge that repeats, and these gating signals respectively all (a) lasting time less than a code element, (b) equal forward and negative sense area are arranged, and (c) have the positive or negative polarity corresponding at the center with the trend of the plus or minus at PRN sign indicating number edge.
23. the receiver of claim 22, wherein local PRN signal generation apparatus also comprises the device of an initialization collection of the gating signal that repeats that is used for producing non-zero, and these gating signals respectively all (i) lasting time less than a code element, and have (ii) that to represent a PRN sign indicating number edge respectively be just to move towards or the single positive polarity or the negative polarity of negative trend, and wherein each in these a plurality of channel circuits comprises all being used for concentrating from the computing collection of gating signal or initialization and selects a selecting arrangement that carries out mixing with intermediate-freuqncy signal mixer device.
24. the receiver of claim 21, wherein local PRN signal generation apparatus comprises the device of a computing collection that is used for producing the PRN signal, this group PRN signal includes than the 1/2k of the leading above-mentioned code element of phase place of a reference signal and is first reproducing signals of first polarity, than the 1/2k of the above-mentioned code element of phase lag of above-mentioned reference signal and be second reproducing signals with first opposite polarity second polarity, than the leading N/2k of the phase place of above-mentioned reference signal and be the 3rd reproducing signals of above-mentioned first polarity, and than the N/2k of the above-mentioned code element of phase lag of above-mentioned reference signal and be the 4th reproducing signals of above-mentioned second polarity, wherein N and k are integer, and N is less than k.
25. the receiver of claim 24, wherein k equals 10, and N equals 2.
CN96196836A 1995-08-09 1996-08-08 Multipath error reduction in spread spectrum receiver for ranging applications Pending CN1196123A (en)

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US08/512,822 US5953367A (en) 1995-08-09 1995-08-09 Spread spectrum receiver using a pseudo-random noise code for ranging applications in a way that reduces errors when a multipath signal is present
US62074996A 1996-03-11 1996-03-11
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